1. Field of the Invention
The present invention relates to a bicycle transmission mechanism, more particularly to a free-wheel hub transmission mechanism for a bicycle.
2. Description of the Related Art
Referring to FIG. 1, a conventional free-wheel hub transmission mechanism is shown to include an axle 3 and a spoke-mounting barrel 1 mounted rotatably around the axle 3 in such a manner that a right axle portion 300 thereof projects outwardly from a right end portion 100 of the spoke-mounting barrel 1. A sprocket mounting member 5 is sleeved around the right axle portion 300 of the axle 3 adjacent to the right end portion 100 of the spoke-mounting barrel 1. The sprocket-mounting member 5 includes an outer shell 500 that is coupled with the right end portion 100 of the spoke-mounting barrel 1 and that has an inner wall surface 501 formed with a proximate small-diameter wall section 502 and a distal large-diameter wall section 503. Left and right bearing units 6 are disposed inside the large-diameter wall section 503 of the outer shell 500 and around the right axle portion 300 of the axle 30. A positioning tubular sleeve 7 is disposed within the large-diameter wall section 503 of the outer shell 500 around the right axle portion 300 of the axle 3 in such a manner that two opposite ends of the tubular sleeve 7 abut against the left and right bearing units 6, respectively, in order to prevent axial displacement of the left and right bearing units 6 relative to each other. A clutch assembly 4 is disposed inside the right end portion 100 of the spoke-mounting barrel 1 and is operably coupled with the outer shell 500 so as to permit co-rotation of the spoke-mounting barrel 1 with the sprocket mounting member 5 in only a single direction.
Some of the drawbacks of the aforementioned conventional free-wheel hub transmission mechanism are as follows:
It is somewhat difficult to assemble the components of the aforesaid hub transmission mechanism. During assembly, the axle 3 is inserted through the spoke-mounting barrel 1 in such a manner that the right axle portion 300 projects outwardly from the right end portion 100 of the spoke-mounting barrel 1. The sprocket mounting member 5 is then mounted around the right axle portion 300 of the axle 3. Because the tubular sleeve 7 is radially displaceable in the outer shell 500 so that just prior to mounting of the sprocket mounting member 5 around the right axle portion 300, the central bores in the bearing units 6 and the tubular sleeve 7 within the outer shell 500 must be aligned with each other to permit smooth extension of the right axle portion 300 therethrough. As such, a relatively long assembly time is thus incurred.